Element, Thin Film Transistor and Sensor Using the Same, and Method of Manufacturing Element

ABSTRACT

Provided is an element which is formed of a conductor composed of a monocrystalline organic compound. Employed is an element including a pair of electrodes with a gap of 10 to 900 nm therebetween and a conductor composed of a monocrystalline organic compound disposed between the pair of electrodes.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an element usable for a thin filmtransistor or a sensor, and a thin film transistor and a sensor usingthe element.

2. Background Art

In the past, a technique of depositing an electrode or an insulatinglayer on previously formed crystals was employed to apply a gate voltageto monocrystals of a molecular conductor (J. S. Brooks, AdvancedMaterials for Optics and Electronics, vol. 8, pp. 269-276 (1998)).However, the technique has a problem that the surface of the organiccrystal is greatly damaged, thereby not fabricating an element havingthe original characteristic of the molecular conductor. This is becausesmooth junction between the crystal and the electrode or the insulatinglayer is necessary for the element using a gate electrode but isdifficult to form.

In this situation, it is considered in S. F. Nelson et al., Appl. Phys.Lett, 72, 1854 (1998) that molecules such as pentacene or polymers suchas polythiophene are deposited on a silicon substrate using a spincoating method to form an element, which is allowed to operate as a thinfilm transistor (FET) However, in this case, domains were formed in theelement and the grain boundaries severely affected the elementcharacteristics. In the molecular conductor, since the molecules aregenerally insoluble in a solvent and do not have malleability orvolatility, at first, such techniques were not able to be applied inalmost all cases.

On the other hand, as a method of educing a conductive material on anelectrode by electrolysis, a method of electrolyzing gold to form apoint contact is disclosed in V. Rajagopalan et al., Nano lett, 3,851-855 (2003). However, in this case, the educed molecules wereamorphous polycrystal and growth of monocrystal has been not known.

A method of electrolyzing phthalocyanine by AC current is disclosed inH. Hasegawa et al., Synthetic Metals, 135-136, 763-764 (2003). However,in this case, electrodes were not bridged.

That is, when an element is fabricated using a polycrystallineconductor, the junction between crystals causes a problem. That is, anunnecessary resistor is generated, a portion operating as a capacitor isgenerated, or a non-linear response such as a Schottky barrier isexhibited. The electrical characteristic of the grain boundary makes theoriginal device characteristic of a monocrystal dull or denatured.Accordingly, it is considered that the original characteristics of thematerial can be sufficiently exhibited if the electrodes are joinedthrough only a monocrystal.

However, as described above, electrodes have not been bridged using amonocrystal.

Here, the inventor eagerly studied the reason for not having been ableto bridge the electrodes using a monocrystal.

First, as a result of study on an inorganic conductor which wasconsidered as a conductor in the past, the inorganic conductor was notsufficient in practice since a very high temperature is necessary toallow the monocrystal to grow between electrodes.

Therefore, the inventor attempted to bridge electrodes using amonocrystal in which an organic material is used as a raw material.However, a monocrystal of a conductor composed of an organic compoundhas not been considered as being used for such an element and a testmethod or a handling method thereof was not clear in many cases. Ofcourse, a method of fabricating a monocrystalline element using anorganic material was not even predicted.

SUMMARY OF THE INVENTION

The present invention is contrived to solve the above-mentionedproblems. An object of the invention is to form a conductor composed ofa monocrystalline organic compound between electrodes.

In this situation, as a result of the inventor's eager study, theabove-mentioned object can be accomplished by the following means:

(1) An element including a pair of electrodes with a gap of 10 to 900 nmtherebetween and a conductor composed of a monocrystalline organiccompound disposed between the pair of electrodes.

(2) An element including a pair of electrodes and a conductor composedof a monocrystalline organic compound disposed between the electrodes,wherein the monocrystalline organic compound is formed by directlygrowing between the electrodes.

(3) The element according to (1) or (2), wherein the conductor consistsof a single piece of monocrystal.

(4) The element according to any one of (1) to (3), wherein theconductor composed of the monocrystalline organic compound is aconductor obtained by forming a salt on the electrodes.

(5) The element according to (4), wherein the monocrystalline organiccompound has an oxidation-reduction potential of 0.8V or less relativeto an Ag/AgCl/CH₃CN electrode.

(5-2) The element according to (4) or (5), wherein the thickness of theelectrodes is in the range of 5 to 20 nm.

(6) The element according to any one of (1) to (3), wherein theconductor composed of the monocrystalline organic compound is aconductor formed by electrolysis on the electrodes.

(6-2) The element according to (6), wherein the thickness of theelectrodes is in the range of 150 to 250 nm.

(7) The element according to (6), wherein the monocrystalline organiccompound contains sulfur.

(8) The element according to (6), wherein the monocrystalline organiccompound is a ring compound.

(9) The element according to (6), wherein the monocrystalline organiccompound is a conjugate organic polymer compound.

(10) The element according to (6), wherein the monocrystalline organiccompound is a cation radical salt or an anion radical salt.

(11) The element according to (6), wherein the monocrystal line organiccompound is one selected from the group consisting of a cation radicalsalt obtained by oxidizing a donor molecule, an anion radical saltobtained by reducing an acceptor molecule, an anion radical saltobtained by partially oxidizing an anion metal complex, and asingle-component molecule obtained by oxidizing an anion metal complexuntil it is neutral.

(12) The element according to (11), wherein the monocrystalline organiccompound is an anion radical salt obtained by reducing an acceptormolecule and a cation radical salt obtained by oxidizing a donormolecule.

(13) The element according to (6), wherein the monocrystalline organiccompound has a tetrathiafulvalene skeleton.

(14) A thin film transistor having the element according to any one of(1) to (13).

(15) A sensor having the element according to any one of (1) to (13).

(16) A method of fabricating the element according to anyone of (1) to(5), the method including forming the conductor composed of amonocrystalline organic compound by forming a salt between the pair ofelectrodes.

(17) A method of fabricating the element according to any one of (1) to(5), wherein a salt is formed between the pair of electrodes out of acompound having an oxidation-reduction potential of 0.8V or lessrelative to an Ag/AgCl/CH₃CN electrode.

(18) The method of fabricating the element according to (16) or (17),wherein an electrode having a lamination structure formed by depositingan electrode material layer other than gold on a gold layer is used asthe electrodes.

(19) A method of fabricating the element according to any one of (1) to(3) and (6) to (13), wherein the conductor composed of a monocrystallineorganic compound is formed between the pair of electrodes by applying avoltage across the pair of electrodes.

(20) The method of fabricating the element according to (19), whereinthe step of forming the conductor composed of a monocrystalline organiccompound between the pair of electrodes by applying a voltage across thepair of electrodes is performed by immersing the pair of electrodes inan electrolyte solution and electrolyzing the electrolyte solution.

(21) A method of fabricating the element according to (1) to (3) and (6)to (13), the method comprising: depositing an electrode layer on asubstrate, immersing the substrate on which the electrode layer isdeposited in an electrolyte solution, and electrolyzing the electrolytesolution by applying a voltage across the electrode layer.

(22) The method of fabricating the element according to (21), whereinthe substrate is a semiconductor substrate.

(23) The method of fabricating the element according to (21) or (22),wherein an insulating layer is formed on the electrode layer.

(24) The method of fabricating the element according to any one of (19)to (23), wherein the electrolyte solution is a solution including oneselected from the group consisting of a donor molecule, an acceptormolecule, and an anion metal complex.

(25) The method of fabricating the element according to any one of (19)to (24), wherein both of the pair of electrodes are positive electrodesor negative electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the entire shape of a substrate beforeelectrolysis in Example 1.

FIG. 2 is a diagram illustrating the entire shape of the substrate afterthe electrolysis in Example 1.

FIG. 3 is a partially enlarged view of FIG. 2.

FIG. 4 is a diagram illustrating a place where a circuit is cut by alaser beam in the substrate shown in FIG. 2.

FIG. 5 is a diagram illustrating the entire shape of a substrate beforefabricating monocrystals in Example 2.

FIG. 6 is a diagram illustrating the entire shape of the substrate afterfabricating monocrystals in Example 2.

FIG. 7 is a partially enlarged view of the monocrystals fabricated inExample 2.

FIG. 8 is a diagram illustrating a place where a circuit fabricated inExample 2 is cut by a laser beam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail. In thefollowing description, “˜” is used to have a meaning including thenumerals described before and after it as the upper limit value and thelower limit value.

First, a monocrystalline organic compound according to the inventionwill be described. As the monocrystalline organic compound according tothe invention, widely known organic compounds can be used if only theyare compounds having conductivity. Examples thereof can include thefollowings.

(1) Organic Compound Containing Sulfur

Organic compounds containing sulfur can be employed and compounds havinga hetero ring skeleton containing sulfur can be used preferably.Compounds including a hetero ring having a carbon number of 3˜10(preferably a carbon number of 4˜6) containing one or more sulfur and acondensed ring in which the hetero ring and/or two or more other ringshaving a carbon number of 3˜10 (preferably a carbon number of 4˜6) arecondensed can be used more preferably. The number of condensed rings ispreferably in the range of 2˜15, more preferably in the range of 2˜10,still more preferably in the range of 2˜5, and still more preferably inthe range of 2˜4. The condensed rings may be bonded to each otherthrough a single bond, a double bond, a triple bond, or a connectiongroup. Examples of the connection group can include two-valence or moremetal atoms, —CH₂—, —O—, —S—, or —N—, and groups obtained by combinationof two or more thereof. Examples of the hetero ring forming thecondensed ring can include rings having a thiophene skeleton, adithiophene skeleton, a thiazole skeleton, and a thiane skeleton and/ora dithiane skeleton. The compounds containing sulfur according to theinvention may have a proper substituent group without departing from thegist of the invention.

Preferable examples of the organic compound containing sulfur accordingto the invention can include compounds having a tetrathiafulvalene (TTF)skeleton or compounds having a dithiophene metal skeleton(M(dmit)₂)(wherein M is Ni, Pd, or Pt). As the compounds having thetetrathiafulvalene (TTF) skeleton, tetrathiafulvalene (TTF),ethylendithio-tetrathiafulvalene (EDT-TTF), andbis(ethylendithio)-tetrathiafulvalene (BEDT-TTF) can be used preferablyand ethylendithio-tetrathiafulvalene (EDT-TTF) can be used morepreferably.

(2) Ring Compound

Ring compounds can be employed, which preferably includes hetero ringcompounds. As the ring compounds, compounds having a condensed ring inwhich two or more ring compounds having a carbon number of 3˜10(preferably a carbon number of 4˜6) are condensed can be usedpreferably. The number of condensed rings is preferably in the range of2˜15, more preferably in the range of 2˜10, still more preferably in therange of 2˜5, and still further preferably in the range of 2˜4. Thecondensed rings maybe bonded to each other through a single bond, adouble bond, a triple bond, or a connection group. Examples of theconnection group can include two-valence or more metal atoms, —CH₂—,—O—, —S—, and —N—, and groups obtained by combination of two or morethereof. Ring-type hydrocarbons and/or hetero rings are preferably usedas the compound forming the condensed ring. The ring compounds accordingto the invention may have a proper substituent group without departingfrom the gist of the invention.

Preferable examples of the ring compound according to the invention caninclude compounds having a benzene skeleton, compounds having a quinoideskeleton, compounds having a triphenylene skeleton, compounds having aperylene skeleton, compounds having a rubicene skeleton, compoundshaving a coronene skeleton, compounds having an ovalene skeleton, andcompounds having a hetero ring skeleton. More preferable examplesthereof can include compounds having a quinoide skeleton, compoundshaving a perylene skeleton, and compounds having a hetero ring skeleton.

Examples of the compounds having a quinoide skeleton can include7,7,8,8-tetracyanoquinondimethane (TCNQ) and dicyanoquinondiimine(DCNQI).

In addition, compounds which are exemplified in the above (1) andcorrespond to the ring compounds can be preferably used. (3) ConjugateOrganic Polymer

Conjugate organic polymers can be used and examples thereof can includepolyacetylene, polythiophene, poly(3-methythiophene),polyisothianaphthene, poly(p-phenylene sulfid), poly(p-phenylene oxide),polyaniline, poly(p-phenylene vinylene), poly(thiophene vinylene),polyperinaphthalene, nickel phthalocyanine, polydiacetine, polypyrrol,polyparaphenylene, polyparaphenylene sulfide, and polyacrylate.

In addition, compounds which are exemplified in the above (1) or (2) andcorrespond to the conjugate organic polymers can be preferably used.

(4) Cation Radical Salt

A cation radical salt according to the invention is preferably obtainedby oxidizing a donor molecule. The donor molecule is not particularlylimited so long as it does not depart from the gist of the invention.However, preferable examples thereof can include compounds having atetrathiafulvalene (TTF) skeleton, compounds having a perylene skeleton,and compounds having a tetrathiapentalene (TTP) skeleton and morepreferable examples thereof can include compounds having atetrathiafulvalene (TTF) skeleton and compounds having a peryleneskeleton.

Compounds which are exemplified in the above (1) to (3) and correspondto the cation radical salts can be preferably used.

(5) Anion Radical Salt

A conductor composed of a monocrystalline organic compound can beobtained by an anion radical salt. The anion radical salt according tothe invention can be obtained preferably by reducing an acceptormolecule or partially oxidizing an anion metal complex. Among them, theanion radical salt can be obtained more preferably by reducing anacceptor molecule.

The acceptor molecule according to the invention is not particularlylimited so long as it does not depart from the gist of the invention,but preferable examples thereof can include a variety of substituted7,7,8,8-tetracyanoquinondimethane (TCNQ), dicyanoquinondiimine (DCNQI),and a variety of substituted quinones (chloranil, etc.) and morepreferable examples thereof can include a variety of substituted7,7,8,8-tetracyanoquinondimethane (TCNQ) and a variety of substituteddicyanoquinondiimine (DCNQI).

On the other hand, the anion metal complex is not particularly limitedso long as it does not depart from the gist of the invention, butpreferable example thereof can include compounds having a dithiolenemetal skeleton (M(mnt)₂) (wherein M is Ni, Pd, or Pt) (M(dmit)₂)(wherein M is Ni, Pd, or Pt)and a phthalocyanine complex and morepreferable example thereof can include compounds having a dithiolenemetal skeleton(M(dmit)₂) (wherein M is Ni, Pd, or Pt).

Compounds which are exemplified in the above (1) to (3) and correspondto the anion radical salt can be preferably used. (6) Single-componentMolecular Conductor obtained by oxidizing Anion Metal Complex until itis neutral

A single-component molecular conductor obtained by oxidizing an anionmetal complex until it is neutral can be employed. Here, the usableanion metal complex is not particularly limited so long as it can becomea single-component molecular conductor by oxidizing a complex until itis neutral and widely known complexes can be used. A specific examplethereof can include Ni(tmdt)₂.

Compounds which are exemplified in the above (1) to (5) and correspondto the single-component molecular conductor obtained by oxidizing ananion metal complex until it is neutral can be preferably used.

The conductor composed of a monocrystalline organic compound accordingto the invention means that a composition exhibiting conductivity iscomposed of a monocrystalline organic compound, but does not excludethat another component (for example, materials, impurities and the likeused for fabricating a conductor) is included therein without departingfrom the gist of the invention.

Preferable compounds can be properly selected from the compounds of (1)to (6), depending upon the applications and the like. For example, whenit is used in a thin film transistor or a sensor, the compounds of (1)and (2) having a relatively high resistance can be preferably used. Onthe other hand, when it is used for a wire material, the compound of (3)having a relatively low resistance can be preferably-used.

The material of the electrode according to the invention is notparticularly limited, but a variety of materials can be used so long asthey do not depart from the spirit of the invention. Preferable examplesthereof can include gold (Au), titanium (Ti), chromium (Cr), tantalum(Ta), copper (Cu), aluminum (Al), molybdenum (Mo), tungsten (W), nickel(Ni), palladium (Pd), platinum (Pt), silver (Ag), and tin (Sn). Inaddition, conductive polymers such as polythiophene (specifically,polyethylene dioxythiophene), polystyrensulfonate, polyaniline,polypyridine, polyphenylene vinylene doped with pyrrole and iodine, andpolyethylene dioxythiophene/polystyrene sulfonate compolymer can beused. Furthermore, combinations thereof can be used. For example,combinations (for example, lamination structure) of gold (Au) and othermetals (preferably titanium (Ti), nickel (Ni), and copper (Cu)) can beused. The gap between the electrodes is preferably in the range of 10 to900 nm, more preferably in the range of 50 to 500 nm, and still morepreferably in the range of 50 to 200 nm.

The conductor composed of a monocrystalline organic compound accordingto the invention is allowed to directly grow between the electrodesformed on an electrode layer after the electrode layer is formed on asubstrate. Here, “directly grow” means that monocrystals are allowed togrow between the electrodes, not that monocrystals are formed and thenthe monocrystals are joined to electrodes. By using such a means, it ispossible to smooth the junction between the monocrystals and theelectrodes. The growth of a conductor composed of a monocrystallineorganic compound can be carried out by forming a salt using a solutionincluding an organic compound for forming the monocrystals between theelectrodes or by electrolyzing the electrolyte solution.

First, the method of forming the salt using the solution including anorganic compound for forming the monocrystals between the electrodeswill be described. Such a solution is not particularly limited so longas it can form a monocrystalline salt between the electrodes byimmersing the electrodes in the solution or dropping the solutionbetween the electrodes and then drying the electrodes. Specifically,compounds having an oxidation-reduction potential of 0.8V or lessrelative to an Ag/AgCl/CH₃CN electrode can be preferably used, compoundshaving an oxidation-reduction potential of 0.5V or less relative to anAg/AgCl/CH₃CN electrode can be more preferably used, acceptor moleculescan be still more preferably used, and a derivative of DCNQI or TCNQ ismost preferably used. Of course, compounds which are the above (1) to(6) and can form the salt between the electrodes are preferably used.

The concentration of the organic compound in which the electrodes areimmersed is preferably in the range of 0.1 to 20 mmol/L and morepreferably in the range of 0.5 to 5 mmol/L. By setting the range ofconcentration as described above, the monocrystals can properly growbetween the electrodes. A solvent dissolving the organic compound is notparticularly limited so long as it does not depart from the gist of theinvention, but preferable examples thereof can include acetonitrile,acetone, chloroform, and benzonitrile. When the salt is formed byimmersing the electrodes (and the substrate on which the electrodes areformed) in the solution, the immersing time is preferably in the rangeof 10 to 120 seconds. By setting the range of time as described above,it is possible to allow proper monocrystals to grow between theelectrodes.

When the monocrystals are formed by forming the salt, the thickness ofthe electrodes is preferably in the range of 5 to 20 nm. By setting therange of thickness of the electrodes as described above, it is possibleto allow crystals to more properly grow between the electrodes. When themonocrystals are formed by forming the salt, it is preferable that theelectrodes having a lamination structure in which an electrode materiallayer other than gold is formed on a gold layer. By using such theelectrodes, it is possible to effectively avoid electricalnon-connection due to dissolution of the electrodes. In this case, theabove-mentioned materials of the electrodes can be preferably used asthe electrode materials laminated on the gold layer.

On the other hand, when the fabrication is carried out by electrolyzingan electrolyte solution, the electrolyte solution is preferably asolution including a solution of donor molecules, acceptor molecules,and anion metal complexes. Of course, compounds which are the above (1)to (6) and can form the monocrystals by electrolysis can be preferablyused. The solvent used for the electrolyte solution is not particularlylimited so long as it does not depart from the gist of the invention,but preferable examples thereof can include ethanol, methanol,chlorobenzene, dichloromethane, and mixtures thereof. The electrolysiscan be performed by applying a voltage across the electrodes. Thevoltage applied for the electrolysis is preferably in the range of 750to 1100 mV. In the electrodes, it is more preferable that crystals areallowed between the positive electrode and the positive electrode orbetween the negative electrode and the negative electrode than thatcrystals growing from the positive electrode (or negative electrode) arejoined to the negative electrode (or positive electrode). That is, forexample, by forming electrodes on the silicon substrate (of which thesurface is made of SiO₂) and performing the electrolysis into theelectrolyte solution using the electrode as the positive electrode, themonocrystals composed of an organic compound grows so as to bridge theelectrodes. By using such a means, it is possible to more effectivelyprevent crystals from being collected too densely, thereby allowing themonocrystals to more smoothly grow. It is preferable that a gateelectrode is used as the opposite-polarity electrode at the time ofelectrolysis. By using the gate electrode as the opposite-polarityelectrode, it is possible to allow the monocrystals to grow moreuniformly. When the monocrystals are formed by electrolysis, thethickness of the electrodes is preferably in the range of 150 to 250 nm.By setting the thickness of the electrodes as described above, it ispossible to easily bridge the electrodes, thereby allowing themonocrystals to easily grow.

When single crystals are formed by electrolysis, an insulating layer maybe formed on the electrodes. By forming the insulating layer, it isdesirable to exclude current flowing in the crystals disposed on theside surfaces of the electrodes and not serving as the conductor. Thethickness of the insulating layer is preferably in the range of 15 to 25nm. The insulating layer can be made of a variety of materials so longas it does not depart from the spirit of the invention. For example,inorganic materials such as silicon oxide, silicon nitride, aluminumoxide, titanium oxide, and calcium fluoride, polymer materials such asacryl resin, epoxy resin, polyimide, and Teflon (registered trademark),and self-organizing molecular films such as aminopropyl ethoxysilane canbe preferably used.

When a substrate is provided in the element according to the invention,the substrate is not particularly limited, and well known substrates canbe widely used. Examples thereof can include an insulating substrate anda semiconductor substrate.

The insulating substrate can be made of, for example, insulating resinsuch as silicon oxide, silicon nitride, aluminum oxide, titanium oxide,calcium fluoride, acryl resin, and epoxy resin, polyimide, Teflon, andthe like.

The semiconductor substrate can be made of, for example, silicon,germanium, gallium arsenide, indium phosphide, and silicon carbide, andpreferably silicon. The surface of the substrate is preferably flat.

Since the element according to the invention can be fabricated on thesemiconductor substrate, a gate voltage can be applied thereto. As aresult, it is possible to fabricate a thin film transistor.

In the element according to the invention, by burying agate electrodeunder the substrate, it is possible to fabricate the element to which agate voltage can be applied. The material of the gate electrode is notparticularly limited, and the materials used for such a type oftransistors in the past can be widely used. Examples thereof can includeAl, Cu, Ti, polysilicon, silicide, and organic conductive material. Thegate insulating layer can be formed of, for example, inorganicinsulating materials such as SiO₂ and SiN or an organic material such aspolyimide and polyacrylonitrile.

In this way, the element according to the invention can be used for athin film transistor. The substrate and the insulating layer can employthe above-mentioned materials.

EXAMPLES

Hereinafter, the invention will be described in more details withreference to examples. Materials, amounts thereof, ratios, processingdetails, processing procedures, and the like described in the followingexamples can be properly changed without departing from the gist of theinvention. Accordingly, the scope of the invention is not limited to thespecific examples described below.

Example 1

1. Fabrication of Electrode Layer

A positive type resist (ZEP) was applied to a silicon substrate (made byFuruuchi Chemical Corporation) of which the surface is coated with anoxide film and a circuit shown in FIG. 1 was drawn thereon using anelectron beam lithography apparatus (Elionix 7300). The resultantstructure was developed with pentyl acetate and then a titanium layerwith 50 Å, a gold layer with 1500 Å, and a silicon dioxide layer with 20Å were deposited thereon. A liftoff process was performed thereto with2-butanone. In this way, the electrode layer shown in FIG. 1 wasfabricated.

2. Adjustment of Electrolyte Solution

12 mg of EDT-TTF produced using the method described in Chem. Lett, Vol.1989, p 781, 20 mg of tetraphenyl phosphonium bromide (Tokyo ChemicalIndustry T1069), 80 mg of tetraiodoethylene (TIE) (Aldrich 31824-8), and2 ml of methanol were added to 18 ml of chlorobenzene, were agitatedwell, and then were left alone a night.

3. Fabrication of Monocrystal using Electrolysis

2 ml of the electrolyte solution was put into a glass petri dish and thesilicon substrate fabricated in 1 was immersed in the solution. A powersource was connected to a gold pad on the substrate using a prober(Kyowariken K-157MP). The electrodes shown in FIG. 1 were disposed sothat a concave electrode shown below serves as a negative electrode anda skewer-shaped electrode shown above serves as a positive electrode. Inthis state, an electrolysis process was performed for 1 minute byapplying a voltage of 800 mV thereto while monitoring current.Thereafter, the substrate was rapidly taken out and the remainingsolution was removed. When the substrate having been sufficiently driedwas observed using an electron microscope, a plurality of smallmonocrystals of (EDT-TTF)₄Br₃(TIE)₅ was created as shown in FIG. 2. FIG.3 is an enlarged photograph illustrating the portion indicated by anarrow in FIG. 2 and it could be confirmed from the photograph thatmonocrystals firmly bridge the electrodes.

4. Check of Electrical Connection

It was confirmed that current of about 50 nA flows when burning off theportion indicated by the arrow in FIG. 4 and applying a bias voltage of1V across both the electrodes.

Example 2

1. Fabrication of Silicon Substrate

A resist (PMMA/MMA) was applied to a silicon substrate of which thesurface is coated with an oxide film and a circuit shown in FIG. 5 wasdrawn thereon using an electron beam lithography apparatus (Elionix7300). The resultant structure was developed and then a titanium layerwith 50 Å, a gold layer with 150 Å, and a copper layer with 100 Å weredeposited thereon. A liftoff process was performed thereto with acetone.In this way, the electrode layer shown in FIG. 5 was fabricated.

2. Adjustment of Solution

15 mg of dimethyl-N,N′-dicyanoquinondimine (DMe-DCNQI) (made of AldrichCorporation) was added to 20 ml of nitrile acetate and then was agitatedwell.

3. Fabrication of Monocrystal

2 ml of the prepared solution was put into a glass petri dish and thesilicon substrate fabricated in 1 was immersed in the solution for 30seconds. Since it can be observed using an electron microscope that finecrystals grow on the substrate, the substrate was taken out when crystalgrows with a proper density and then was dried. It was confirmed thatmonocrystals were created as shown in FIG. 6. FIG. 7 is an enlargedphotograph of FIG. 6 and it could be confirmed from the photograph thatmonocrystals firmly bridged the electrodes.

4. Check of Electrical Connection

It was confirmed that current flows when properly burning off thecircuit fabricated above using a laser beam and checking the electricalconnection thereof. For example, when fabricating the four-terminalcircuit shown in FIG. 8 and measuring the resistance values thereof, theresistance of the crystals was about 5 kΩ and the contact resistancewith the electrode was about 1 kΩ.

INDUSTRIAL APPLICABILITY

In the present invention, it was possible to succeed in fabricatingmonocrystals composed of an organic compound and to accomplish theelectrical connection between the electrodes. In the past, elementsformed of a conductor other than conductors having organic compounds orpolycrystalline elements were known, but the element including theconductor composed of a monocrystalline organic compound as in theinvention was not known at all. No test method was suggested for theconductor composed of monocrystalline organic compounds.

However, the inventor completed such an element through his energeticstudy, which is very great.

As described later, in the element according to the invention, sinceconductivity can be measured using one monocrystal, it is possible toprevent unbalance between elements. As a result, it is possible tofurther enhance operational performance.

In the method according to the invention, since the element can befabricated on a silicon substrate and the like, as well as on a glasssubstrate, it is possible to fabricate a circuit including a gateelectrode using a molecular conductor.

In the conductor composed of a monocrystal organic compound, since aconstituent element is a “molecule”, functional groups having a varietyof functions can be introduced and we can expect characteristicsdifferent from inorganic devices of the known inorganic elements areexhibited. Specifically, since an element is based on a monocrystalhaving a very clear structure, it is possible to accomplish highlysensitive and precise characteristics of an element and to accomplishapplications to a very large range of fields.

In the method according to the invention, a monocrystal can be createddirectly on an electrode. Accordingly, since the monocrystal grows alongthe surface shape of the silicon substrate, it is possible to form ajunction with a highly planarity by only planarizing the surface of thesilicon substrate, compared with the known technique of junction aninsulating film using a spattering method. Therefore, it is possible touse a conductor composed of an organic compound for an element withoutbeing affected by grain boundaries.

The element according to the invention can be used for a thin filmtransistor having a high-speed response characteristic or ahigh-sensitivity sensor reacting to light, humidity, or pH. By employingan element in which (preferably 1000 or more) monocrystals are arrangedin parallel, it is possible to embody a sensor capable of sensing a veryweak signal.

1-25. (canceled)
 26. An element including a pair of electrodes with agap of 10 to 900 nm therebetween and a conductor composed of amonocrystalline organic compound disposed between the pair ofelectrodes.
 27. An element including a pair of electrodes and aconductor composed of a monocrystalline organic compound disposedbetween the electrodes, wherein the monocrystalline organic compound isformed by directly growing between the electrodes.
 28. The elementaccording to claim 26, wherein the conductor consists of a single pieceof monocrystal.
 29. The element according to claim 26, wherein theconductor composed of the monocrystalline organic compound is aconductor obtained by forming a salt on the electrodes.
 30. The elementaccording to claim 29, wherein an organic molecule constituting themonocrystalline organic compound has an oxidation-reduction potential of0.8V or less relative to an Ag/AgCl/CH₃CN electrode.
 31. The elementaccording to claim 26, wherein the conductor composed of themonocrystalline organic compound is a conductor formed by electrolysison the electrodes.
 32. The element according to claim 31, wherein themonocrystalline organic compound contains sulfur.
 33. The elementaccording to claim 31, wherein the monocrystalline organic compound is aring compound.
 34. The element according to claim 31, wherein themonocrystalline organic compound is a conjugate organic polymercompound.
 35. The element according to claim 31, wherein themonocrystalline organic compound is a cation radical salt or an anionradical salt.
 36. The element according to claim 31, wherein themonocrystalline organic compound is one selected from the groupconsisting of a cation radical salt obtained by oxidizing a donormolecule, an anion radical salt obtained by reducing an acceptormolecule, an anion radical salt obtained by partially oxidizing an anionmetal complex, and a single-component molecule obtained by oxidizing ananion metal complex until it is neutral.
 37. The element according toclaim 36, wherein the monocrystalline organic compound is an anionradical salt obtained by reducing an acceptor molecule and a cationradical salt obtained by oxidizing a donor molecule.
 38. The elementaccording to claim 31, wherein the monocrystalline organic compound hasa tetrathiafulvalene skeleton.
 39. A thin film transistor having theelement according to claim
 26. 40. A sensor having the element accordingto claim
 26. 41. A method of fabricating the element according to claim26, wherein including forming the conductor composed of amonocrystalline organic compound between the electrodes.
 42. The methodaccording to claim 41, wherein the conductor composed of amonocrystalline organic compound is formed by forming a salt between thepair of electrodes.
 43. The method according to claim 41, wherein a saltis formed between the pair of electrodes out of a compound having anoxidation-reduction potential of 0.8V or less relative to anAg/AgCl/CH₃CN electrode.
 44. The method according to claim 41, whereinan electrode having a lamination structure formed by depositing anelectrode material layer other than gold on a gold layer is used as theelectrodes.
 45. The method according to claim 41, wherein the conductorcomposed of a monocrystalline organic compound is formed between thepair of electrodes by applying a voltage across the pair of electrodes.46. The method according to claim 45, wherein the forming of theconductor composed of a monocrystalline organic compound between thepair of electrodes by applying a voltage across the pair of electrodesis performed by immersing the pair of electrodes in an electrolytesolution and electrolyzing the electrolyte solution.
 47. The methodaccording to claim 41, wherein the method comprising: depositing anelectrode layer on a substrate, immersing the substrate on which theelectrode layer is deposited in an electrolyte solution, andelectrolyzing the electrolyte solution by applying a voltage across theelectrode layer.
 48. The method according to claim 47, wherein thesubstrate is a semiconductor substrate.
 49. The method according toclaim 47, wherein an insulating layer is formed on the electrode layer.50. The method according to claim 46, wherein the electrolyte solutionis a solution including one selected from the group consisting of adonor molecule, an acceptor molecule, and an anion metal complex.
 51. Amethod according to claim 45, wherein both of the pair of electrodes arepositive electrodes or negative electrodes.